Extension of potentialities of millisecond pulsed Nd:YAG lasers in the welding technology

The dependences of the dynamic parameters of the growth of a vapour-gas channel and the depth of the melting zone on the shape of laser pulses and the spatial beam parameters are studied. Based on this study, the requirements are formulated to the characteristics of radiation providing a many-fold increase in the melting depth with respect to the depth that was previously considered as limiting. A new laser setup for deep high-quality welding was built. The role of the buffer volume of a melt in the suppression of ejection of molten metal from the laser-heated region upon deflection of the melt surface is substantiated. An increase in the rate of growth of a vapour-gas channel during an increase in its length (the self-concentration of a heat source) was experimentally observed. At the depths corresponding to the preferential vertical orientation of fluid flows, a large-scale vortex motion of the melt was observed. The dependence of the penetration depth of the melting front on the aperture angle β was experimentally found to have an extremum. The maximum penetration depth was obtained for β = 0.075 — 0.80 rad. Recommendations for designing pulsed laser technological systems for high-quality welding of metals are formulated.